The invention relates to substrate processing, and more particularly to transferring substrates to and from processing chambers.
Glass substrates are being used for applications such as active matrix televisions and computer displays, among others. A large glass substrate can form multiple display monitors, each of which may contain more than a million thin film transistors.
The processing of large glass substrates often involves the performance of multiple sequential steps, including, for example, the performance of chemical vapor deposition (CVD) processes, physical vapor deposition (PVD) processes, or etch processes. Systems for processing glass substrates can include one or more process chambers for performing those processes.
The glass substrates can have dimensions, for example, of 550 mm by 650 mm. The trend is toward even larger substrate sizes, such as 650 mm by 830 mm and larger, to allow more displays to be formed on the substrate or to allow larger displays to be produced. The larger sizes place even greater demands on the capabilities of the processing systems.
Some of the basic processing techniques for depositing thin films on the large glass substrates are generally similar to those used, for example, in the processing of semiconductor wafers. Despite some of the similarities, however, a number of difficulties have been encountered in the processing of large glass substrates that cannot be overcome in a practical way and cost effectively by using techniques currently employed for semiconductor wafers and smaller glass substrates.
For example, efficient production line processing requires rapid movement of the glass substrates from one work station to another, and between vacuum environments and atmospheric environments. The large size and shape of the glass substrates makes it difficult to transfer them from one position in the processing system to another. As a result, cluster tools suitable for vacuum processing of semiconductor wafers and smaller glass substrates, such as substrates up to 550 mm by 650 mm, are not well suited for the similar processing of larger glass substrates, such as 650 mm by 830 mm and above. Moreover, cluster tools require a relatively large floor space.
One way to improve such processing tools is disclosed in U.S. patent application Ser. No. 08/946,922, entitled xe2x80x9cMODULAR CLUSTER PROCESSING SYSTEM,xe2x80x9d assigned to Applied Komatsu Technologies, Inc. of Santa Clara, Calif., and incorporated above by reference. The use of a modular processing system is disclosed, with substrate movement exterior of processing islands performed by conveyors or robots on tracks. Substrate movement interior of processing islands is performed by a substrate transporter. In this type of system, the transporter may move a substrate into or out of a processing chamber, after which the transporter may stay resident in either load lock.
Similarly, chamber configurations designed for the processing of relatively small semiconductor wafers are not particularly suited for the processing of these larger glass substrates. The chambers must include apertures of sufficient size to permit the large substrates to enter or exit the chamber. Moreover, processing substrates in the process chambers typically must be performed in a vacuum or under low pressure. Movement of glass substrates between processing chambers, thus, requires the use of valve mechanisms which are capable of closing the especially wide apertures to provide vacuum-tight seals and which also must minimize contamination.
Furthermore, relatively few defects can cause an entire monitor formed on the substrate to be rejected. Therefore, reducing the occurrence of defects in the glass substrate when it is transferred from one position to another is critical. Similarly, misalignment of the substrate as it is transferred and positioned within the processing system can cause the process uniformity to be compromised to the extent that one edge of the glass substrate is electrically non-functional once the glass has been formed into a display. If the misalignment is severe enough, it even may cause the substrate to strike structures and break inside the vacuum chamber.
Other problems associated with the processing of large glass substrates arise due to their unique thermal properties. For example, the relatively low thermal conductivity of glass makes it more difficult to heat or cool the substrate uniformly. In particular, thermal losses near the edges of any large-area, thin substrate tend to be greater than near the center of the substrate, resulting in a non-uniform temperature gradient across the substrate. The thermal properties of the glass substrate combined with its size, therefore, makes it more difficult to obtain uniform characteristics for the electronic components formed on different portions of the surface of a processed substrate. Moreover, heating or cooling the substrates quickly and uniformly is more difficult as a consequence of its poor thermal conductivity, thereby reducing the ability of the system to achieve a high throughput.
As noted above, efficient production line processing requires rapid movement of the glass substrates from one work station to another. Other requirements include a structure that can firmly support the glass substrate during transfer and that can transport the glass substrate to all areas of a work station or processing island.
The present invention allows large glass substrates to be moved within a processing station and from one processing station to another. In systems according to the invention, at least a first and second chamber are provided. Typically, the first chamber is a load lock and the second chamber is a processing chamber. The processing chamber may serve as an inspection station, a CVD chamber, a PECVD chamber, a PVD chamber, a post-anneal chamber, a cleaning chamber, a descumming chamber, an etch chamber, or a combination of such chambers. The load lock may be employed to heat or cool the substrate. Two load locks may be employed, one to perform heating and the other to perform cooling. The load locks each include a platen for supporting the substrate.
A substrate transfer shuttle is used to move substrate along a guide path defined by, e.g., guide rollers.
The substrate transfer shuttle is moveable along a linear path defined by guide rollers between one position in the first chamber and another position in the second chamber. In this way, the substrate may be transferred, in both a forward and a reverse direction, between the first chamber and the second chamber. The substrate transfer shuttle is structured so that a substrate may be removed therefrom by moving the platen from a lowered position to an intermediate position, after which the substrate transfer shuttle may be removed from the processing chamber. The substrate transfer shuttle includes first and second longitudinal side rails at respective first and second sides thereof. The shuttle also includes first and second pluralities of substrate support elements extending inwardly from the first longitudinal side rail and positioned to pass below the substrate when the substrate transfer shuttle is removed from the processing chamber. The substrate support elements extend about 15-30% of a dimension of the substrate, and more particularly about 22% of the width of the substrate. Drive mechanisms are employed that engage with at least the first longitudinal side rail to move the substrate transfer shuttle along at least portions of the shuttle path.
Implementations of the invention may include one or more of the following. A valve may be employed to selectively seal the first chamber from the second chamber when closed and to permit transfer of the substrate between the first chamber and the second chamber through the valve when open. Multiple shuttles may be employed for convenience in a particular process. Further, multiple intermediate chambers may be located between the first and second chambers.
The susceptor in the processing chamber includes a plurality of lift pins which are movable through holes in the susceptor and which support the substrate above the susceptor.
Steps of the method include positioning a substrate onto a substrate transfer shuttle in a load lock, and moving the substrate transfer shuttle from the load lock into a processing chamber along a first portion of a path. The substrate is removed from the substrate transfer shuttle and positioned it on a platen in the processing chamber. The substrate transfer shuttle is then removed from the processing chamber and the substrate is processed. Following processing, the substrate transfer shuttle is moved into the processing chamber and the substrate is positioned thereon. The substrate transfer shuttle and the substrate are moved into the load lock, and the substrate is removed from the substrate transfer shuttle.
Advantages of the invention include one or more of the following. The invention eliminates unnecessary substrate movement in a semiconductor processing system. For example, the substrate may be transferred horizontally except for loading and unloading on the susceptor. The invention also eliminates more expensive and cumbersome vacuum robots and transfer chamber systems. The invention allows removal of a substrate transfer shuttle during processing, reducing contamination.